Membrane fluidity

In biology, membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the membrane. Viscosity of the membrane can affect the rotation and diffusion of proteins and other bio-molecules within the membrane, there-by affecting the functions of these things. Membrane fluidity is affected by fatty acids. More specifically, whether the fatty acids are saturated or unsaturated has an effect on membrane fluidity. Saturated fatty acids have no double bonds in the hydrocarbon chain, and the maximum amount of hydrogen. The absence of double bonds decreases fluidity, making the membrane very strong and stacked tightly. Unsaturated fatty acids have at least one double bond, creating a "kink" in the chain. The double bond increases fluidity. Membrane fluidity is also affected by cholesterol. Cholesterol can make the cell membrane fluid as well as rigid. Factors determining membr

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Cholesterol Hinders the Passive Uptake of Amphiphilic Nanoparticles into Fluid Lipid Membranes

Ester Canepa, Matteo Gasbarri, Giulia Rossi, Francesco Stellacci

Plasma membranes represent pharmacokinetic barriers for the passive transport of site-specific drugs within cells. When engineered nanoparticles (NPs) are considered as transmembrane drug carriers, the plasma membrane composition can affect passive NP internalization in many ways. Among these, cholesterol-regulated membrane fluidity is probably one of the most biologically relevant. Herein, we consider small (2-5 nm in core diameter) amphiphilic gold NPs capable of spontaneously and nondisruptively entering the lipid bilayer of plasma membranes. We study their incorporation into model 1,2-dioleoyl-sn-glycero-3-phosphocholine membranes with increasing cholesterol content. We combine dissipative quartz crystal microbalance experiments, atomic force microscopy, and molecular dynamics simulations to show that membrane cholesterol, at biologically relevant concentrations, hinders the molecular mechanism for passive NP penetration within fluid bilayers, resulting in a dramatic reduction in the amount of NP incorporated.

AMER CHEMICAL SOC2021

Monitoring the Cellular Cholesterol Distribution via NanoSIMS Imaging

Mustafa Demir

Cholesterol is a very crucial lipid for animal cells, since it is the building block of cellular membranes, control fluidity of membranes, regulate intracellular transport, cell signalling, nerve conduction and serve as a precursor for synthesis of vitamin D and steroid hormones. Cholesterol is such an important biological molecule for animal cells, yet it has been a real challenge so far, to understand distribution of cholesterol within the biological membranes. In our study, using ultra-high resolution ion microprobe (NanoSIMS) imaging enables us to detect incorporated cholesterol in cells, introduced as 13C labeled cholesterol, in nanometer scale. Then, we are able to monitor the localization of detected cholesterol in cellular structures by combining NanoSIMS (Secondary Ion Mass Spectrometry) with electron microscopy. Our aim in this study is to determine level of incorporated cholesterol in cellular membranes, secretion and endocytic systems, by the help of NanoSIMS imaging combined with electron microscopy.

2015

The influence of 0-0.1 wt.% Ni on the microstructure and fluidity length of Sn-0.7Cu-xNi

Michel Rappaz, Tina Ventura

Alloys based on the Sn-0.7Cu-xNi system are potential Pb-free solders. In this paper we report on the solidification characteristics and microstructures of Sn-0.7Cu alloys containing 0-1,000 ppm nickel. The microstructural observations show that increasing the nickel content reduces the volume fraction of primary Sn, thus generating a more-eutectic microstructure. In an attempt to better understand the changes in solderability with Ni additions, fluidity tests were carried out using the Ragone method for small incremental increases in nickel content. The maximum fluidity length was found to vary strongly with nickel content. Additionally, the distribution of nickel within samples was investigated using synchrotron micro X-ray fluorescence.

Springer Verlag2008

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